A technology is provided, in which a raw material of a water-soluble organic matter which forms an azeotrope with water and the azeotrope of which with water has a lower boiling point than water, such as isopropyl alcohol (hereinafter, also referred to as “IPA”), or a water-soluble organic matter having a lower boiling point than water is dehydrated by a process combining separation by distillation using a distillation column with membrane separation using a vapor-permeation separation membrane (hereinafter, also referred to as a hybrid process) (for example, refer to Patent Literature 1). It is known that such a hybrid process can save energy more largely than conventional dehydration only by distillation.
Pressure distillation or atmospheric pressure distillation is used as a method for separation by distillation. When the pressure distillation is combined with a separation membrane, column top vapor of a distillation column is treated directly by a vapor-permeation separation membrane. On the other hand, when the atmospheric pressure distillation is combined with a separation membrane, column top vapor is pressurized by a vapor compressor, and then is treated by a vapor-permeation separation membrane. The hybrid process combining the pressure distillation with the vapor-permeation separation membrane is industrialized, for example, in dehydration of bioethanol.
When an organic matter is dehydrated and condensed so as to have a high purity using a current hybrid process, high selectivity, high permeability, or the like with respect to water is required as performance of a vapor-permeation separation membrane. For example, when IPA is dehydrated and condensed to about 99.0% by mass of the total mass, in general, a vapor-permeation separation membrane having a permeability ratio (also referred to as permeance ratio) between IPA and water in the order of several hundreds and having permeability (also referred to as permeance) of water of about 10−6 mol/m2·Pa·s or more, is necessary. The higher the permeability ratio is, the higher the energy saving performance of the whole process is.